EVAP Purge Test Using Special Equipment

The most accurate method of checking EVAP purge flow is to check the system in the same manner in which it was tested. EVAP purge flow testers (sometimes combined with pressure testers) are currently available from aftermarket sources and typically operates as follows:

1. Precondition the vehicle by running the engine until it reaches operating temperature.

2. Connect the tester's flow transducer into the EVAP purge line between the engine and evaporative canister.

3. With the engine off, zero the tester to calibrate the purge flow reading.

4. Next, with the engine idling, start the timer and observe the purge flow rate and accumulated purge volume on the tester display.

Note: On TVV equipped systems that use a ported vacuum purge source, no purge should take place during idle, however, on systems using a VSV, the ECM may command a very slight amount of flow during idle.

5. Slowly raise engine speed and maintain a steady 2500 rpm. During this period purge flow should increase dramatically and, on a properly functioning EVAP system, 1 liter of flow should be surpassed in a matter of seconds.

6. If the system does not flow at least 1 liter within the 240 second test period or it marginally passes the test, perform the following functional checks to help identify the suspect parts or components.

Note: Since most vehicles flow 25 liters or more during the same period, marginal passes should also be checked and repaired since these systems are not functioning properly and will probably fail in future tests.

7. Once the problem has been identified and repaired, perform this test again to confirm sufficient improvements in purge volume.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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